1. Field of the Invention
The present invention relates to a structure allowing for detection of a load applied to a vehicle seat. In particular, the invention is directed to such load detection structure for use in a vehicle seat.
2. Description of Prior Art
Recent years have witnessed a tendency for various automatically controlled functions and mechanisms to be increasingly incorporated in vehicle or automobiles, including safety devices such as air bags for protecting passengers against a great impact automatically in response to a collision, as well as various kinds of seat position adjustment devices for automatically adjusting the positions of seat sensitive to driver""s or passenger""s physiques and seating conditions. With such automated control innovations, there have been also found technical improvements to a passenger detection system for detecting the presence and absence of a passenger or driver in a seat of vehicle in advance before actuating or stopping the associated mechanical elements to automatically control various functions and mechanisms built in the seat.
Normally, the passenger detection system employs various sensors (e.g. a pressure sensitive element) which detect the weight of a passenger on a seat and emit a signal to electronic control systems for automatic control of various mechanical elements related to the seat. Most of the sensors are of a simple structure which can only sense the presence and absence of passenger on a seat, but the recent high-tech control technology inevitably requires that the sensors should further detect whether the passenger is an adult or a child as with an air bag control system for instance.
To meet the demand, there have been proposed sensor systems for numerically detecting the weight of passenger or a corresponding load applied to the seat, determining whether the passenger is adult or child, according to a numerical data obtained, and then controlling and adjusting the associated mechanical elements to optimal conditions suited for the adult or child (e.g. controlling air bag), as disclosed from the Japanese Laid-Open Patent Publications Nos. 11-001153 and 11-304579. Namely, the Japanese Laid-Open Patent Publication No. 11-001153 shows a combination of an impact sensor and four load sensors, wherein each of the four load sensors is interposed between a slide rail device on which the seat is mounted and a support leg member fixed on the floor of vehicle. It also suggests an H-shaped base plate on which wiring of the load sensors is collectively arranged for electrical connection with another one cable. According thereto, the weight of an occupant on the seat is detected by the four load sensors in a collision case, and a signal emitted therefrom is determined by a control unit as to the numerical amount of the occupant""s weight, so that the air bag is adjusted in inflation according to the numerical data on the occupant""s weight, thereby realizing a proper inflation of air back to protect the occupant optimally according to his or her physique. On the other hand, the Japanese Laid-Open Patent Publication. No. 11-304579 discloses plural link mechanisms each having an arm pivoted therein, the link mechanisms being arranged between a slide rail fixed to a seat and a support base fixed on the floor of vehicle. In this prior art, a load sensor is provided at the free end portion of each arm of the link mechanism, such that a load applied vertically to the seat is imparted through the pivoted arm as an amplified or reduced vertical motion to the load sensor which then detects the amount of such vertical motion and determine a total weight of the seat and occupant on the seat. This reference states that a signal corresponding to the total weight may be emitted from the load sensors to a control unit associated with air bag and seat adjustment device, for instance.
However, the Japanese Laid-Open Patent Publication No. 11-001153 has no description regarding the mechanical structure of load sensor itself, and has no specific teaching on how the load sensor structurally supports the seat and how it actions to detect the seat occupant""s weight. This prior art is therefore neither realistic nor practical in assembling an optimal mechanical structure between the sensor and seat. The Japanese Laid-Open Patent Publication No. 11-304579 is found defective in that its link mechanism and pivoted arm are complicated in structure and further they occupy much of space heightwise between the seat and slide rail device, which results in the seat becoming large vertically in size and increasing its weight. Consequently, there remains a room of improvement in materializing a simplified and effective structure for this sort of load detection system. Furthermore, as with those prior arts, most of conventional load detection structures are adapted to only detect a vertically applied load, which are not provided with any means for preventing a twisting deformation of the load sensors. For, such twisting deformation will occur when the seat is subjected to lateral inclination due to irregular vibration of vehicle running on a rough and curved road as well as the weight of seat occupant being excessively applied in one of the rightward and leftward directions relative to the seat. In that case, the load sensors can not precisely detect the amount of load and it is of a high likelihood that an air back or seat adjustment mechanism connected to the sensors will not be controlled well to cause an inconvenience and trouble to the seat occupant.
In view of the above-stated drawbacks, it is therefore a primary purpose of the present invention to provide an improved load detection structure which is greatly simplified in structure with reduced number of constituent elements and effective in avoiding undesired increase in height of the seat.
In order to achieve such purpose, according to the present invention, the load detection structure in combination with a vehicle seat having a seat cushion and a support leg means, includes a load detection means for detecting a load applied from a seat occupant to the vehicle seat, the load detection means comprising:
a block member having an elongated body extending in the longitudinal direction thereof, the block member having a rigid yet elastically deformable property and including, defined therein, a securing portion, a pivotal end portion, and a thin intermediate portion between the securing portion and pivot end portion, wherein the pivotal end portion has an upper side formed lower than an upper side of the securing portion, and the thin intermediate portion is defined by forming a recession in an upper side region of the block member in a direction transversely thereof at a point between the securing portion and pivotal end portion;
a strain gauge means fixedly attached to the thin intermediate portion of block member;
a vertically guiding and connecting means provided in the securing portion of block member, the support leg member, and a bottom side of seat cushion, the vertically guiding and connecting means being for securely connecting the securing portion of block member with a bottom side of the seat cushion and allowing vertical displacement of the securing portion between the bottom side of seat cushion and the support leg means; and
the block member being interposed between the bottom side of seat cushion and the support leg means in such a manner that the securing portion of block member is securely connected with the bottom side of seat cushion via the vertically guiding and connecting means, whereas the pivotal end portion of block member is pivotally connected with the support leg means at a predetermined pivot point,
wherein, when a downward load is applied to the seat in a vertical direction, the securing portion of block member is displaced in a generally rectilinear downward direction, while at the same time, the pivotal end portion of block member is rotated about the pivot point, whereupon a difference is caused in movement and direction between the securing portion and the pivotal end portion, which results in a deflection of the thin intermediate portion, and, in response thereto, the strain gauge detects an amount of the deflection and emits a corresponding value indicative of an amount of the load.
Accordingly, the block member is subjected to vertical deflection only within the height-wise range between the bottom side of seat cushion and support leg member. Thus, such heightwise thin construction does not lead to increase in height of the seat and it is possible to keep the seat situated at as low level as possible with reference to a vehicle floor. Furthermore, there is eliminated the need to provide a great number of intricate parts and fittings for assembling the load detection structure in the seat as found in the prior art.
In one aspect of the present invention, a twist prevention means may be provided in the pivotal end portion of block member, which twist prevention means allows the block member to be rotatable and inclinable about a central axis thereof in one of two symmetrical directions relative to a central line of the support leg member in response to a lateral load being applied to the seat in one of leftward and rightward directions intersecting the vertical direction of said downward load, to thereby prevent the thin intermediate portion of the block member from being twisted by the lateral load.
In another aspect of the invention, an auxiliary linkage means may be pivotally provided between the bottom side of seat cushion and the support leg means, which auxiliary linkage is so pivotally movable as to aid in only vertical movement of the seat cushion or the vehicle seat to and from the support leg means, thereby preventing the thin intermediate portion of block member from being twisted by the lateral load.
Other various features and advantages of the invention will become apparent from reading of the descriptions hereinafter, with reference to the annexed drawings.